All those grant-givers, Arts Council grandees, intellectual-wannabe celebs and assorted boosters who, every so often (usually around Poetry Day), crawl out of whatever piece of bureaucratic woodwork they normally inhabit to proclaim that poetry in Britain has never been more vibrant, diverse and popular should remember two things: that Britain's greatest living poet is actually a soi-disant Irishman; and that, of all sales of poetry books by living writers in Britain, the same man, Seamus Heaney, alone accounts for almost two-thirds.

Those two factlets spell a grave crisis in British poetry. The latter for fairly obvious reasons: because of its perennially low sales figures, poetry is desperately unattractive to bookshops, which naturally prefer to stick with established authors; and while the number and quality of reviews for new poetry in the mainstream press have declined to the point of invisibility, publishers are failing to back up their books with decent PR. When was the last time you walked past a Waterstone's or Borders and saw some grand point-of-sale promo for a new volume of poetry? The result is a vicious circle of neglect for new work, unless it be by one of the very few big names that the form can boast. Poetry thus becomes the furtive preserve of those who would gladly let the likes of Heaney and Ted Hughes (dead, but still selling well) have what little limelight there is so that they can indulge their geeky, cultish obsession with the difficult and the wilfully obscure.

The other factor is related, but more complex, and it has to do with the current fetishisation of the Celtic fringes as a kind of ur-culture from which the British (for which read English) mainstream has been diverted. Nowhere is this embodied more clearly than in the arc of Heaney's charmed career. Born into a Catholic farming family in County Derry, Heaney was described early on by no less a figure than Robert Lowell as "the most important Irish poet since Yeats". He has been garlanded with prizes, including the Nobel, and laden with acclaim.

All criticism of his lack of political engagement with the land of his birth evaporated in 1975 after the publication of North, with its combination of pastoral imagery and political encryptions. Then, in the early 1980s, Heaney refused permission for his work to be included in a Penguin anthology of British verse. By way of explanation, he wrote the following lines in a pamphlet at around the same time: "Be advised, my passport's green/No glass of ours was ever raised/ To toast the Queen."

On the surface, it was simply a statement of his own reconfigured national identity, a planting of a flag - and, as such, appealed to those in Britain, particularly on the left, who were ashamed of the way the British state went about defending its sway in Ulster. But it was also an act of recreancy, because, in the glib opposition it set up, it disavowed any possibility of ever recasting the British state in non-monarchical terms.

The ultimate accolade came in 1995, with the award of the Nobel Prize. That set the seal on the whole "Famous Seamus" phenomenon, whereby every droning pub bore boasts of being on nodding terms with the bard from the valley of the Bann. Heaney himself seems highly uncomfortable with this - he is unable in interviews to utter the word Nobel, referring to it as "the Stockholm thing" or "the N-word" - and clearly sees it as an impediment to the privacy and anonymity that a poet needs to do his work.

Yet, unwitting as it may be, he has taken an important place in the construction of a new romanticised Oirishness that is now all-pervasive, through the proliferation of themed pubs, the endless export of pretty boy bands, newspaper paeans to the Celtic Tiger economy and the idea of the Irish as the new Jews - with their historic burden of oppression to shoulder, representing an authenticity, a connection to the land and to their own story that we cynical metropolitan sophisticates have long since lost. Ah sure, 'tis an improvement on the old view of thick Paddy Murphy, but it is no less a stereotype for that.

Electric Light is the second original work from Heaney since he won the Nobel. In between, he has produced little apart from his acclaimed translation of Beowulf, that foundation stone on which the edifice of English literature is built. Taking their cue from a phrase in that translation, critics have talked swooningly ever since about Heaney's "word-hoard", in much the same way people used to go on about Linford Christie's "lunchbox", citing it as an emblem of his poetic virility. No doubt, they will find much to praise in these poems, which return again to the Bann Valley of the poet's childhood, but which also range throughout Europe, to the Balkans and to Greece, as well as through time, particularly to the classical world. And like some 1960s Vegas show host, Heaney gives the obligatory nods to departed greats such as Ted Hughes, Joseph Brodsky, Zbigniew Herbert, so that one can almost hear the ripple of audience applause at the mention of each name.

Reading Heaney, I have often felt as if I were being forced by some crusty old uncle to wear a particularly scratchy woollen jumper that doesn't quite fit under the arms. This book is no exception, the compressed textures of the language taking primacy over just about everything else.

Take these lines, which begin the title poem: "Candle-grease congealed, dark-streaked with wick-soot./The smashed thumb-nail/Of that ancient mangled thumb was puckered pearl,/Rucked quartz, a littered Cumae." Or these, in a poem about perch in the Bann river, where Heaney writes of "little flood-slubs, runty and ready", of watching them "guzzling in the current, against it, all muscle and slur/In the finland of perch, the fenland of alder, on air/That is water". This, surely, is poetry that has had half a bottle of whiskey too much: one certainly admires the artistry in the wreathing of the words, but one fears to get too close to the man that breathes them.

The sense of emotional disengagement - which for me is ever-present in Heaney's work - is heightened by the use of easy-seeming classical references. Here, they appear in Arcadian abundance, from Virgil walking in the Bann Valley to six sonnets from Greece (or "Hellas", as the sequence title insists). Faber's blurb writer tells us that this is Heaney exploring "the places where things start from, the ground of understanding". But equally it reads like a claim being staked, a self-conscious demand for a place within the canon that stretches back to Virgil and beyond. Well, perhaps Heaney has done enough to earn that; but for those toiling eternally on the lower slopes of Parnassus - the ones who make up the other third of the British poetry market - it begins to look as if he doesn't have to try too hard any more.